Uninterruptible Power Supply

February 2017

Introduction to Uninterruptible Power Supply

An uninterruptible power supply (UPS) is a device that protects electronic equipment from power uncertainties. A UPS is a device that is interfaced between the electric network (connected to utility power) and the materials that need protecting.

The UPS allows the materials to be switched to emergency battery power for several minutes in case of electrical problems, in particular during:

  • Power line disturbances, i.e. a split second power outage that can cause a computer to restart
  • Power outages, corresponding to a break in the power supply for a given amount of time
  • Overvoltage, i.e. a nominal value greater than the maximum value needed for the normal functioning of electrical appliances
  • Undervoltage, i.e. a nominal value less than the maximum value needed for the normal functioning of electrical appliances
  • Voltage spikes, i.e. high amplitude transient (short-term) overvoltage. These spikes are caused when powerful devices are stopped or started and overtime can damage electrical components
  • Lightening, which is a source of extreme overvoltage that occur suddenly during bad weather (storms)

Most electrical disruptions are tolerated by computer systems. However, sometimes they can cause data loss and service interruptions and even material damages.

The UPS helps to "smooth out" voltage, i.e. eliminate peaks that are over a certain level. When there is a power outage, the energy stored in the emergency battery keeps the power supply flowing to equipment for a small amount of time (normally for 5 to 10 minutes). Beyond the minutes of autonomy that the UPS supplies, this gained time also allows the equipment to be switched to other energy sources. Some UPSs can also be directly attached to the computer (e.g. with a USB cable) so that it can order its own shutting off in case of a power outage and thus avoid any data loss.

Types of UPS

There are generally three types of UPSs:

  • "Offline" UPSs are connected via an electrical relay. When all is functioning properly, the voltage from the electric network is used to recharge the batteries. When the voltage goes above or below a certain level (maximum or minimum), the relay opens and the voltage is recreated using the energy stored in the battery. Because of the time it takes to open and close the relay, this type of UPS does not protect against power line disturbances
  • "Online" UPSs are connected in series and constantly regulate voltage
  • "Line interactive" UPSs are a hybrid technology. Line interactive UPSs are connected parallelly via a relay but have a microprocessor that continuously monitors the voltage. In case of a weak drop in voltage or a power line disturbance, the UPS is able to inject voltage to compensate. In the case of a total power outage, however, the UPS functions like an offline UPS.

Characteristics of an Uninterruptible Power Supply

The length of electrical protection by a UPS is expressed in VA (Volt-Ampere). Generally, for electrical protection during a 10-minute power outage, you must have a UPS with a capacity that is equal to the power of all the materials connected to the UPS multiplied by a factor of 1.6.

When choosing a UPS, it is also important to check the number of sockets it has.

Sometimes UPSs have connectors (USB, network, parallel, etc.) that make it possible to connect them with the CPU so that it can order its own shutting off in case of a prolonged power outage and backup all the work in progress.

It should be noted that UPSs do not protect telephone connections. Therefore, a computer connected to a UPS as well as a modem may still be damaged if lightening hits a telephone line.

Self-sufficiency Rooms

For those companies where a constant supply of energy is of critical importance, it is possible to set up a series of UPSs in a room called the "self-sufficiency room".

These rooms are generally equipped with dozens or even hundreds of UPSs that are capable of providing an electrical supply during a power outage lasting several hours. "Self-sufficiency" rooms may also include a generator that can take over after the UPSs have run out of power.


Fuente de alimentación ininterrumpible
Fuente de alimentación ininterrumpible
Gruppo statico di continuità
Gruppo statico di continuità
Ondulador (UPS)
Ondulador (UPS)
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